The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
Some tooth problems cause sharp, shooting pain and some cause dull aches. Some tooth pain comes and goes and some is persistent and difficult to relieve. Throbbing tooth pain is often associated with inflammation in or around the tooth caused by: 1  infection in the center (the pulp) of the tooth. 2  infection of the gums. 3  sinus infection. 4  cracked or chipped teeth. 5  broken crowns or fillings.